1. Field of the Invention
The present invention relates to a method and a process for building tyres for vehicle wheels.
The present invention also relates to a plant for building tyres for vehicle wheels, usable for carrying out the aforementioned process.
2. Description of the Related Art
Tyre production cycles envisage that, after a building process wherein the various components of the tyre itself are made and/or assembled in one or more assembly lines, a moulding and vulcanization process is carried out in a suitable vulcanization line, suitable for defining the tyre structure according to desired tread geometry and design.
A tyre generally comprises a toroidally ring-shaped carcass including one or more carcass plies, strengthened with reinforcing cords lying in substantially radial planes (a radial plane contains the rotation axis of the tyre). Each carcass ply has its ends integrally associated with at least one metal reinforcing annular structure, known as bead core, constituting the reinforcing of the beads, i.e. the radially inner ends of the tyre, having the function of enabling the assembling of the tyre with a corresponding mounting rim. Placed crown wise to said carcass is a band of elastomeric material, called tread band, within which, at the end of the moulding and vulcanization steps, a raised pattern is formed for ground contact. A reinforcing structure, generally known as belt structure, is arranged between the carcass and the tread band. Such structure usually comprises, in the case of tyres for cars, at least two radially overlapped strips of rubber fabric provided with reinforcing cords, usually of metal, arranged parallel to each other in each strip and crossed with the cords of the adjacent strip, preferably symmetrically arranged with respect to the equatorial plane of the tyre. Preferably, the belt structure further comprises in a radially outer position, at least on the ends of the underlying belt strips, also a third layer of textile or metal cords, arranged circumferentially (at 0 degrees).
Finally, in tyres of the tubeless type, a radially inner layer, called liner, is present which has imperviousness features for ensuring the air-tightness of the tyre itself.
To the aims of the present invention and in the following claims, by the term “elastomeric material” it is intended a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such composition further comprises additives such as cross-linking and/or plasticizing agents. By virtue of the cross-linking agents, such material may be cross-linked by heating, so as to form the final manufactured article.
In the present context, by the term “green tyre” it is indicated a tyre obtained by the building process and not moulded and vulcanized yet.
In the present description and in the following claims, by “elementary component” it is meant an elementary semi-finished product in the form of at least one of the following: a continuous elongated element of elastomeric material; a rubber metal or textile reinforcing cord, that is coated with elastomeric material; a ribbon-like element of elastomeric material cut to size comprising at least two textile or metal cords, hereinafter called “strip-like element”.
In the present description and in the following claims, by “structural component” of the tyre it is meant any part of the tyre suitable for carrying out a function or a portion thereof. For example, structural components therefore are the liner, the under-liner, the abrasion-proof element, the bead core, the bead filler, the carcass ply, the belt strip, the belt under-layer, the tread band under-layer, the sidewall inserts, the sidewalls, the tread band, the reinforcing inserts.
In the present description and in the following claims, by the term “managing” it is meant an operation of movement within the building plant, or of support and/or of holding in stand-by during the building.
WO 2009/040594, by the same Applicant, describes a plant and a process for producing tyres for vehicle wheels, said process comprising the steps of:
a) building a carcass structure of a green tyre on a first forming drum in at least one line for assembling the carcass structure, said carcass structure comprising at least one carcass ply and a pair of anchoring annular structures;
b) building a crown structure of a green tyre on at least one second forming drum in at least one line for building the crown structure, said crown structure comprising at least one belt structure and a tread band;
c) toroidally shaping said carcass structure assembling it to said crown structure in at least one station for assembling and shaping the tyre being processed, said assembly and shaping station being synchronised with said line for building the carcass structure and with said line for building the crown structure;
wherein each carcass structure is associated with the respective first forming drum whereon it is built till the end of step c) of shaping and assembly the tyre being processed;
d) moulding and vulcanizing the green shaped tyre in at least one line for moulding and vulcanizing the tyre separate from said assembly and shaping station.
WO 2008/099236 by the same Applicant, describes a forming drum for building tyres having at least one outer surface and provided with auxiliary support elements capable of being moved in a removable manner close to the forming drum on axially opposite sides and having respective support surfaces that extend axially in the prosecution of the outer surface.
In the plants of the type described in WO 2009/040594, it is often necessary to dispense elementary components in zones axially external to the forming drum. Therefore, it is necessary to support such elementary components that would otherwise deflate around the forming drum itself. To this end, the Applicant has noted that it is possible to use forming drums and auxiliary support elements of the type described in WO 2008/099236.
The Applicant has further verified that in building plants of this type, using forming drums and auxiliary support elements associable with them, managing drum transfers is often complex as it also comprises managing the transfers of the relative auxiliary support elements.
Moreover, in such cases, work stations are poorly accessible by the operators, who should instead be able to move easily in order to ensure proper plant operation and suitable maintenance of the same.